The total solar eclipse will cast a shadow across a band of the country stretching from Oregon to South Carolina, depriving the nation's solar farms of their fuel. The event isn't expected to create any trouble keeping the lights on, but it will force many states to turn to other energy sources to fill the void left by sun-starved solar farms.

Since there's essentially no marginal cost once a wind tower or solar farm is installed — the wind blows for free and there's no price for sunshine — electrons produced by renewable power plants tend to be the first to meet electricity demand. Grids then tap natural gas, nuclear power, coal and other resources to meet their remaining needs.

Translation: The eclipse gives plants that run on nonrenewable resources a chance to make some extra scratch on Monday.

This total eclipse is unique because it's the first to occur over the United States since states started connecting utility scale solar plants to their power grids. Each of these plants feed the electricity grid with at least 1 megawatt of power, enough to power about 1,000 homes, depending on region and other factors.

The eclipse will obscure 70 percent or more of the sunlight over utility-scale power plants that account for nearly half of the nation's major solar power capacity, according to the U.S. Energy Information Administration.

The state, which can produce enough solar power to supply 600,000 houses on a sunny day, will have natural gas-fired plants ready to start turning turbines, according to Duke.

Natural gas plants can quickly feed the fossil fuel into their facilities and address spikes in demand. On extraordinarily hot summer days and during winter chills, they stand to make a lot of money.

Many of California's solar farms are outside the most affected area. But the state's 8.8 gigawatts of utility-scale solar capacity makes up 40 percent of total U.S. capacity, so the Golden State has been preparing for the eclipse since last year. The grid operator, California Independent System Operator, thinks it will lose about 6 gigawatts of capacity from solar farms and rooftop panels.

It says it will turn to fuel sources that can most easily ramp up to meet demand: hydro power and natural gas-fired plants. Luckily, the eclipse dovetails with the high water season, making it easier to draw on more hydro power.

A group of 13 eastern states and Washington, D.C., could lose as much as 2,500 megawatts of solar power, according to PJM Interconnection, which operates the grid for Pennsylvania, New Jersey, Maryland and all or part of nearby states.

There's only about 500 megawatts of solar power that feed directly into PJM's grid, but rooftop solar panels generate about 2,000 megawatts of energy within its jurisdiction. PJM said it will be monitoring demand from these homes and businesses so that it's better prepared for the next eclipse, which is expected in 2024.